Format PullUpdated, and keep the announced base head on a rechecked member

A head checked again through mesh-delivery reached the direct verdict with no
base head, so a head no build judges was answered with no trunk commit and the
merge tool would refuse it (novox/hq ADR 0323).

cmd/mesh-controller/delivery.go

@@ -580,6 +580,9 @@ type orderMember struct {
 	CloneURL       string   `json:"clone_url,omitempty"`
 	// After are the repositories its pull request says it goes after (`after: <repository>`).
 	After []string `json:"after,omitempty"`
+	// BaseSHA is the base branch's head the forge last announced the head with (novox/hq ADR 0323): the trunk commit
+	// a verdict no build judges names when the head is checked again through mesh-delivery.
+	BaseSHA string `json:"base_sha,omitempty"`
 }
 
 // pull is the member as the forge announced it.
@@ -589,7 +592,7 @@ func (m orderMember) pull() link.PullUpdated {
 	if base == "" {
 		base = "main"
 	}
-	return link.PullUpdated{Owner: owner, Repo: repo, Number: m.Number, Base: base, Commit: m.Head,
+	return link.PullUpdated{Owner: owner, Repo: repo, Number: m.Number, Base: base, Commit: m.Head, BaseSHA: m.BaseSHA,
 		CloneURL: m.CloneURL, Paths: m.Paths, PathsTruncated: m.PathsTruncated, Removed: m.Removed,
 		ModuleDirs: m.ModuleDirs, ModuleDirsSaid: m.ModuleDirsSaid}
 }